Biliary excretion of iopanoate glucuronide by the rat

Biliary excretion, plasma decay, and tissue distribution of 125I after a single intravenous dose (13 mumol/kg) of 125I-Iopanoate and 125I-iopanoate glucuronide were compared in control and phenobarbital-pretreated rats under either anesthesia. In control animals the plasma decay of iopanoate glucuronide following iopanoate glucuronide administration was significantly greater than that after iopanoate administration. Biliary clearance following iopanoate glucuronide was approximately 20 times greater than that after iopanoate; within 60 min, 82% of the dose of iopanoate glucuronide, compared to 23% of the dose of iopanoate, was recovered in bile. Phenobarbital pretreatment significantly increased the biliary excretion following iopanoate administration but had no effect on that following iopanoate glucuronide. The urinary excretion after both agents was less than 3% of the administered dose within the 60-min experimental period. The data suggest that intracellular metabolism and/or binding may account for the marked difference in the biliary excretion of iopanoate glucuronide following iopanoate as compared to that after administration of iopanoate glucuronide.